Modified latex



Patented Jan. 15, 1946 MODIFIED LATEX Duncan W. MacLeod, Boston, Mass, assignor to General Latex and Chemical 0011)., Cambridge, Y Mass, a corporation of Massachusetts No Drawing. Application July 24, 1943, -Serial N0.496,067

4Cla-ims. (Cl. 260815) This invention relates to the modification of latex so as to render it extremely sensitive to certain chemical influences, and to methodsof using such modified latex in the manufacture of various types of articles, the present application being a continuation-in-part of application Serial No. 237,461, filed October 28, 1938.

The usual latices of commerce, without regard to concentration, are quickly and completely coagulated by the addition of small concentrations of divalent ions such as Ca++, Zn++. They are not appreciably affected by any monovalent ion in concentrations below 5% in the water phase except H+ and Li+. Substantially insoluble compounds of divalent metals, such as zinc benzoate, etc., have little efiect on them in the cold.

However, I have discovered that such latices, when properly compounded with one or'more of a group of certain aromatic compounds, hereinafter more specifically defined, are very sensitive to the action of certain monovalent ions other than H-lor Li+ and certain water insoluble latex non-coagulants. Specifically, my sensitized or modified latex is greatly thickened by the addition of such insoluble material or of such monovalent ions even in concentrations much below 5% in the water phase of the latex. Under special conditions, thickening can be carried so far as to produce an apparently solid wet deposit as, for example, upon a form. These sensitizing materials I call modifiers and these thickening agents developers.

The terms modifiers and modifying agents are used synonomously, and each connotes aromatic hydrocarbons which are substantially insoluble in dilute aqueous ammonia and which, per se, exhibit no thickening efiect on latex, their hydroxy and amino derivatives, and the aromatic ketones, ethers and sulphoxides.

All such modifying agents appear to act by adsorption at the interface between the individual rubber particles and the external water phase. They appear to change or modify the charge distribution of the particles so that the comparatively low potential developer ions are enabled to easily neutralize the remaining partiole-changes and thereby thicken the latex.

The compounds of the following groups have been found operative as modifiers:

Group A p-hydroxydiphenyl p.p"-Dihydroxydipheny1 Di ip-hydroxyphenyl) -1, 1-cyclohexane CH -CHPOQO p-Hydroxyazobenzene D 2,4-diaminodiphenylamine Diphenylamine p.p'-Diaminodiphenylmethane Diphenyl oxide Diphenyl su'lphoxide Diphenylene oxide p-Diphenyl benzene p-Cyclohexyl phenol Diphenyl sulphide When compounded with latex which contains no developer, from 0.1 to of any oneor more of the modifying agents listed in Group'sfA and B will modify the latex as torender it capable of being thickened at room temperatures on the addition of the developer. Thickening in the cold can thus be effected without the use of heated forms and with amounts of developer too small to impair the desirable properties ofthe rubber articles produced from-the latex.

Addition of any one of these modifiers alone to latex will not produce thickening or coagulation under any circumstances. For example, a latex containing '4-%-of any modifier listed may be heated for substantial times at temperatures at or near the boiling-point-of water without viscosity change smthat heat which'calls forth the dormant coagulation'propertiesof some materials has no such effect onthese. Moreover a very large amount of modifier will not cause thickening or coagulation. A 60%centrifuged latex containing 100 dry parts of di- (p.hydroxyphenyl)- 1,1-cyclohexaneshowed no viscosity change after two months room storage temperature.

Since all of the modifiers "listed are substantially water insoluble, Ihave "foundit convenient to ball mill them separately andto add the Diphenyl ball milled dispersion to latex., l'fihereafter, modificationproceeds at a measurable rate depending upon thecha-racter and concentration of the modifying'agent, the length-of. time ball milled, the temperature at which modification be carried out, and the previous historyefthe l'atex.

The longer the modifier hasbeen ball milled the more rapid will bethe rate at which it modifies or sensitizes "the latex. The rate of modification is also increased by heating the latex compounded with the modifier.

The term developer? asherein used, connotes both organic andinorganic compounds capable of acting onthesensitizd'latex so as to produce substantial-thickening.

Developers for amodified latex'need not be coagulants or thickeners for ordinary latex. I have found that the oxides of zinc, cadmium and copper, and the zinc, cadmium or copper salts of weak organic acids suchas .benzoic, tartaric or citric acid readily thickentthemodifiedlatex but have substantially no effectaipon the regular unmodified product, '.-e. g.,-normali and concentrated latex.

However, that developer which have-foundv of most use in the practice of my invention is the zinc-ammonia complex. It may be prepared by dissolving parts of zinc chloride or zinc benzoate in 75 parts of 26 lBaum ammonium hydroxide solution. a

In addition to its practical-"advantages, this material provides an excellent measure or yardstick of the chemical sensitivity of my new modified latex. For example, a latex which has been modified with about 4% on the dry rubber of any of the modifiers shown in Groups A or B and in which modification has been carried largely or wholly to completion is thickened by the additionof' l'ess than 51% of zinc-ammonia complex, based on the rubber, evenin the'cold; If a-cold form, coated with a dried deposit of zinc-ammonia complex be dipped into a latex modified with any of Group A materials, the latex is so thickened around the form as to produce an apparentlysolid wet :deposit thereon.

In preparinga modified latex in accordance with thepresent invention, the following precautionszshould be borne in mind:

.A .dilute latex may be modified, but dilution after modification destroys some or all of the sensitizing effect.

.Some compounding ingredients must-be used with .care. Fixed .alkalies .such as-sodium hydroxide .or tri sodium phosphate inhibit .modification. -Zinc oxide may .cause premature gelationor coagulation. .For .example,a 60% .ammaniacal latex containing curing ingredients whichtinclude 1% of .zinc oxide :on the dry :rubber as .an activator will coagulate in afew hours after adding 0.4% ofdi- (.p-hydroxyphenyl) -.l.,1- cyclohexane.

If the compounded latex be vulcanized, .how-

evenbe'fore attempted modification, thezinc oxide is rendered-sufficiently inactive .by side reactions, such as those with the accelerator used, as -to allow the modifier to be added without danger ofthickening.

The following examples are illustrative of what is .now considered a satisfactory practice of the invention:

Ezmmplel .-'Moziificution upon stanl'clingaat room temperature To a 60% wilcanizedlatex (TUOJJarts dry rub ber) is added 14 dry parts of di-(p-hydroxyphenyl) -;1;l-icyclohexane from. a "4'0 ball milled dispersion. After standing overnight :at room temperature, modification "is substantially com- Plete.

A cold form is then dipped into an aqueous .developin'gsoiutioncontaining'about 25% of zinca'mmonia complex, dried and then dippedinto the modifiefd'l'atex. In.10'f60 seconds a layer of about 0.020" in'thickness will'have been formed. No deposit is produced upon asimilar formdipped under the same conditions into unmodified latex.

Example .2.-Modificati,on upon heating A 60% centrifuged latex (I00 parts'dry rub her) is heated for /2 hour'at F. with-4 parts of di-(p hydroxyphenyl-1,1 cyclohexane from a 40% ball milled dispersion. "No viscosity change takes place.

The modified latexis' then cooled to room temr. perature and developer equivalent to "(11% zincammon-ia complex on thedry rubber is added, whereupon rapid local ,thickening takes place.

Example Ii-"Dual modification A mixture of 4 parts of ball milled Lithol' Red Toner (containing 30% solids) and 0.5.part of ball milled anti-oxidant (containing 40% solids) is first passed through a=-Premier Mill set at (1.002" and this mixture is then addedto'lfldparts'of 50% vulcanizedlatexivultex). "In case it is desired to remove any coarse. particles of pigment,

Methods of use A modified latex, preferably vulcanized as in Examples 1 and 3, may be employed in the direct production of rubber articles by molding. Within the meaning of this specification a mold is any form, pervious or impervious, which gives the desired shape to a rubber article. For example, a mold may be a dipping form for external molding, an internal mold, a belt or a drum for rubber sheeting, an extrusion orifice or a grooved disk.

The mold is coated or impregnated with the developer. This may be done in any of the usual ways, as, for example, by applying a solution or dispersion of developer to the form and then effecting thickening on the form while it is still wet; or by the application of the developer to the form and drying before use.

The method of applying such modified latex to the coated mold varies with the type of mold. If a coated dipping form is used it is immersed in a bath of latex. If a coated extrusion orifice or die is used, the latex is forced therethrough; if a coated belt is used, the latex may be applied by dipping, flowing or spraying. If it is desired to build up a, comparatively relatively thick article, I prefer to use a solution of zinc-ammonia complex as developer for the coating of the form; if a relatively thin one is desired, I prefer a coating of zinc oxide.

Such modified latex is particularly useful in securing a good rubber-to-metal contact, for example, rubber-coated tool handles, such as pliers and the like, rubber-covered kitchen or household utensils, bottle caps of the crown type, and rubbar-protected metallic surfaces exposed to vapors corrosive of metal but non-corrosive of rubber, such as the vapors of fiuorsilicic acid.

The part of the article to receive the rubber adhesion is new.

In the formation of articles such as thread by extrusion, I prefer to extrude the modified latex through the forming orifice into a solution of the zinc-ammonia complex, instead of forming it through a forming orifice or dies covered with the developer.

Fibrous material of all kinds may be impregnated or coated by means of my new modified latex. In coating, wadding, batting, felted, knittea or woven materials from any kind of fiber,

vegetable, animal or mineral, may be treated with a solution or dispersion of developer which may then be dried or not before application of the modified latex. For impregnation I prefer to impregnate the material with modified latex by immersion to be followed by immersion in a bath of developer. For a superficial coating I prefer to apply a dispersion of zinc oxide as developer to be followed after drying by a spray application of the modified latex.

It is apparent that either the developer or the modified latex may be applied by immersion, flowing or spraying; that the developer may or may not be dried before use; and that the material after the application of the modified latex may or may not be heated.

I have described typical examples of manufacturing processes in which my new material is particularly useful, but such description is to be considered by way of illustration and not by way of limitation.

In the appended claims I use the word latex" to include any natural or artificial dispersion of natural or artificial rubber, whether crude or vulcanized, concentrated or diluted, compounded or uncompounded. By vulcanized latex I mean a latex in which the rubber sulphur combination has proceeded at the least to that point in the rubber particles at which a coagulum formed from those particles will not form a smooth liquid solution in gasoline. Obviously the vulcanization can progress further than this, but at this point vulcanization may be said to begin.

I claim:

1. Latex substantially free of fixed alkali containing 0.1% to 10% of di-(p-hydroxyphenyl) 1,1-cyclohexane, said latex being thickened by the zinc-ammonia complex in an amount less than 1% on the rubber.

2. Latex substantially free of fixed alkali containing 0.1% to 10% of a mixture of p.p'-dihydroxydiphenyl and di- (p-hydroxyphenyl) -1,1-cyclohexane, said latex being thickened by the zincammonia complex in an amount of less than 1% on the rubber.

3. Latex substantially free of fixed alkali containing 0.1% to 10% of a compound selected from a group consisting of p.p-dihydroxydiphenyl, benzidene, p-hydroxydiphenyl, di-(p-hydroxyphenyl) -1,1 cyclohexane, p.p-diaminodiphenylmethane, diphenylamine, p-diphenyl benzene, 2,4- diaminodiphenylamine, diphenyl oxide, diphenyl sulphoxide, diphenylene oxide, dibenzyl, p-hydroxyazobenzene, p-hydroxypropiophenone, di-

-. phenyl, p-cyclohexylphenol, diphenyl sulphide,

said latex being thickened by the zinc-ammonia complex in an amount less than 1% on the rubber.

4. Latex substantially free of fixed alkali modified on heating with 0.1% to 10% of a compound selected from the group consisting of p.p'-dihydroxydiphenyl, benzidene, p-hydroxydiphenyl, di- (p-hydroxyphenyl) -l,1-cycloheXane, p.p'-diaminodiphenylmethane, diphenylamine, p-diphenyl benzene, 2,4-diaminodiphenylamine, diphenyl oxide, diphenyl sulphoxide, diphenylene oxide, dibenzyl, p-hydroxyazobenzene, p-hydroxypropiophenone, diphenyl, p-cyclohexylphenol, diphenyl sulphide, said modified latex being thickened by the zinc-ammonia complex in an amount less than 1% on the rubber.

DUNCAN W. MACLEOD. 

